With development of the information industry, a technology that is capable of transmitting various large amounts of data at high speed has been required. To this end, research has been conducted into a multi-node or multi-cell coordinated transmission method that simultaneously performs communication at multiple nodes using the same resource. In the multi-node or multi-cell coordinated transmission method, the respective nodes perform coordinated transmission, thereby providing higher performance than when signals are transmitted without coordination.
A multi-node system supporting multi-node coordinated communication uses a plurality of nodes, each of which operates as a base station, an access point, an antenna, an antenna group, or a radio remote header (RRH). The nodes may be managed by a base station or a base station controller which controls operations of the nodes or performs scheduling. In the multi-node system, distributed nodes are connected to a base station or a base station controller, which manages a plurality of nodes spaced apart from each other by a predetermined distance or more in a cell, through a cable or a dedicated line. The multi-node system may be considered as a kind of Multiple Input Multiple Output (MIMO) system in that distributed nodes can support a single user equipment or multiple user equipments by simultaneously transmitting and receiving different data streams. In terms of the MIMO system, the multi-node system transmits signals using nodes distributed at various positions. Consequently, a transmission area covered by each antenna is reduced as compared with a centralized antenna system (CAS), and therefore, transmit power can be reduced. In addition, the transmission distance between an antenna and a user equipment is reduced, resulting in a decrease in path loss and enabling data transmission at high speed. This can improve transmission capacity and power efficiency of a cellular system and satisfy communication performance of relatively uniform quality regardless of user locations in a cell. Furthermore, a base station(s) or a base station controller(s) connected to a plurality of distributed nodes cooperate with each other in the multi-node system, and therefore, signal loss is reduced, and correlation and interference between antennas and reduced. According to the multi-node coordinated transmission method, therefore, it is possible to obtain a high signal to interference-plus-noise ratio (SINR).
Consequently, the multi-node coordinated transmission method may be used with or replace the conventional centralized antenna system (CAS) to become a new foundation of cellular communications in order to reduce base station installation cost and backhaul network maintenance cost and, at the same time, to extend service coverage and to improve channel capacity and SINR in a next-generation mobile communication system.
In terms of a standard, MIMO transmission must also be achieved in a multi-node system in order to secure high data capacity required by current and future communication standards. Actually, IEEE 802 and 3GPP, two large standardization organizations, are essentially considering MIMO transmission in a process of discussing a communication standard technology. However, the current communication standards have been designed in consideration of only a CAS. As a result, it is difficult to apply an advanced technology, such as an MIMO technology, to the multi-node system. For development of a future communication system, therefore, it is necessary to establish a communication standard supporting the multi-node system.